By virtue of their good ratio of stiffness and strength to density, composite materials, and in particular core composite structures, find a wide range of applications in the field of aircraft construction. Such composite materials, for example core composite structures, are generally formed from an upper and lower surface layer, or top layer, between which a layer of low bulk density (e.g., of foamed material or a honeycomb core structure, usually filled, formed from vertically running cells of hexagonal cross-section can be located to increase stiffness).
Foamed materials are of interest by virtue of their multi-functionality for application in core composites for large format structural components; e.g., in the field of aviation, and in particular, in component manufacture and in the field of enhanced component properties. For purposes of reinforcing the foam-based core composites, sewing techniques or pre-preg pinning techniques are usually employed, wherein fibres or threads can be inserted into hard foam components. After a resin infiltration process, the regions penetrated by the fibres then contribute to the mechanical reinforcement of the foamed material.
The fibres or threads inserted for reinforcement can take the form of so-called rovings, which consist of parallel running fibres. They can also take the form of threads that consist of twisted or plaited fibres.
In known sewing methods, a needle first punctures the foamed material and penetrates through the latter. At the same time the needle inserts a thread into the foamed material. During insertion into the foamed material, the thread extends parallel to and essentially over the entire length of the needle. The size of the puncture hole is thus determined by the needle diameter and the thickness of the thread.
After withdrawal of the needle from the foamed material or textile, a hole remains, the diameter of which is relatively large compared with the diameter of the inserted thread. The result is that after infiltration with a resin the hole area that is not filled with fibres is filled with resin. This can lead to increased weight of the finished component, which in aviation and space flight, is to be avoided.
DE 10 2005 024 408 A 1 describes the reinforcement of foamed materials by means of a knotting method, in which the needle firstly punctures the material that is to be reinforced (the foamed material), and only then, in the region of the lower face of the foamed material, picks up the semi-finished textile product, and in the following reverse movement pulls it through the punctured hole. In this manner, the hole diameter can be kept relatively small overall.
WO 2007/012353 describes a production method for the reinforcement of core materials for core composites, wherein a hole is firstly punctured in the core composite by means of a gripper, and by means of this gripper a reinforcing material is pulled into the core material. However, the bonding between the reinforcing material and core material can be improved further.